The present invention relates generally to invasive methods for mapping of organs in the body, and specifically to methods for mapping electrical activity in the heart.
Cardiac mapping is used to locate aberrant electrical pathways and currents within the heart, as well as diagnosing mechanical and other aspects of cardiac activity. Various methods and devices have been described for mapping the heart. Exemplary methods and devices are described in U.S. Pat. Nos. 5,471,982 and 5,391,199 and in PCT patent publications WO94/06349, WO96/05768 and WO97/24981, whose disclosures are incorporated herein by reference. U.S. Pat. No. 5,391,199, for example, describes a catheter including both electrodes for sensing cardiac electrical activity and miniature coils for determining the position of the catheter relative to an externally-applied magnetic field. Using this catheter a cardiologist can collect data from a set of sampled points within a short period of time, by determining the electrical activity at a plurality of locations and determining the spatial coordinates of the locations.
Methods of creating a three-dimensional map of the heart based on these data are disclosed, for example, in European patent application EP 0 974 936 and in a corresponding U.S. patent application Ser. No. 09/122,137, which is assigned to the assignee of the present patent application, and whose disclosure is incorporated herein by reference. As indicated in these applications, position coordinates (and optionally electrical activity, as well) are initially measured at about 10 to 20 points on the interior surface of the heart. These data points are generally sufficient to generate a preliminary reconstruction or map of the cardiac surface to a satisfactory quality. The preliminary map is preferably combined with data taken at additional points in order to generate a more comprehensive map. In clinical settings, it is not uncommon to acquire data at 100 or more sites to generate a detailed, comprehensive map of heart chamber electrical activity.
In order to speed up the process of data acquisition, multiple-electrode catheters have been developed to simultaneously measure electrical activity at multiple points in the heart chamber. Such catheters are described, for example, in U.S. Pat. Nos. 5,487,391 and 5,848,972, whose disclosures are incorporated herein by reference. These catheters having multiple electrodes on a three-dimensional structure, which expands inside the heart to take the form of a basket. The basket structure is designed so that when deployed, its electrodes are held in intimate contact against the endocardial surface. A problem with the catheters disclosed in these patents is that they are both difficult and expensive to produce. The large number of electrodes in such catheters is also very demanding of the data recording and processing subsystem. There are additional complexities associated with the deployment and withdrawal of these catheters, and increased danger of coagulation.
U.S. Pat. No. 4,649,924, whose disclosure is likewise incorporated herein by reference, discloses a non-contact method for the detection of intracardiac electrical potential fields. A catheter having an inflatable distal end portion is provided with a series of sensor electrodes distributed over its surface and connected to insulated electrical conductors for connection to signal sensing and processing means. The size and shape of the end portion are such that the electrodes are spaced substantially away from the wall of the cardiac chamber. The sensor electrodes are preferably distributed on a series of circumferences of the distal end portion, lying in planes spaced from each other. These planes are perpendicular to the major axis of the end portion of the catheter.
PCT patent publication WO99/06112, whose disclosure is also incorporated herein by reference, describes an electrophysiological cardiac mapping system and method based on a non-contact, non-expanded multi-electrode catheter. The electrodes on the catheter are used to simultaneously measure the electrical potentials at multiple points on the catheter surface, inside the volume of the heart chamber. To generate the map, these electrical measurements are combined with a knowledge of the relative geometry of the probe and the endocardium. This geometrical knowledge must be obtained by an independent imaging modality, such as transesophogeal echocardiography. Based on the known geometry, Laplace""s equation is solved to find a relation between the potential on the endocardial surface to that on the catheter, in the form of a matrix of coefficients. This matrix is inverted, so as to determine the endocardial potentials based on the electrode potentials. A regularization technique, such as a method of finite element approximation, must be used to ensure proper convergence of the solution.
It is an object of the present invention to provide an improved method for mapping electrical potentials inside a volume, and particularly on a surface bounding the volume.
It is a further object of some aspects of the present invention to provide an improved method for mapping endocardial electrical potentials.
It is still a further object of some aspects of the present invention to provide a method that enhances the speed with which a map of endocardial electrical potentials can be generated.
It is yet a further object of some aspects of the present invention to provide improved methods and apparatus for mapping electrical potentials in the heart while minimizing contact with the endocardium.
In preferred embodiments of the present invention, a mapping probe, preferably a catheter, is inserted into a chamber of the heart, and is used to generate a map of electrical activity over an endocardial surface of the chamber. The catheter comprises one or more position sensors in a distal portion of the catheter, along with a plurality of electrodes, which are distributed over the surface of the distal portion. A geometrical model of the endocardial surface is formed, preferably using the position-sensing capability of the catheter itself, as described, for example, in the above-mentioned U.S. patent application Ser. No. 09/122,137. Electrical potentials within the volume of the chamber are measured using the electrodes on the catheter surface, whose positions are known precisely due to the position sensors in the catheter. The measured potentials are combined with the geometrical model to generate a map of electrical potentials at the endocardial surface.
Preferably, the map is generated by modeling the electric field in the heart chamber as a superposition of fields generated by discrete electric dipoles distributed over the endocardial surface. In this manner, a set of equations is generated, expressing the potential at each of the points on the catheter as a sum of the dipole fields at that point. The set of equations is inverted to find the strengths of the dipoles on the endocardial surface, from which the activation potentials are then determined. The dipole model has been found to give accurate results, while avoiding the heavy computational burden of finite element approximations and other regularization techniques. Alternatively, however, other methods of computation may be used, such as those described in the above-mentioned PCT publication WO99/06112.
Preferably, the electrodes are distributed over the distal portion of the catheter in an array, most preferably a grid array, as described in a U.S. patent application Ser. No. 09/506,766, which is assigned to the assignee of the present patent application, and whose disclosure is incorporated herein by reference. Further preferably, the catheter comprises two position sensors, one near the distal tip of the catheter, and the other near the proximal end of the electrode array, as described in U.S. Pat. No. 6,063,022, which is also assigned to the assignee of the present patent application, whose disclosure is also incorporated herein by reference. Most preferably, the position sensors comprise miniature coils, which are used to determine position and orientation coordinates by transmitting or receiving electromagnetic waves, as described, for example, in the above-mentioned PCT publication WO96/05768 or U.S. Pat. No. 5,391,199. Alternatively, other types of position sensing systems, as are known in the art, may be used.
The present invention thus achieves the combined benefits of non-contact electrical measurement and rapid mapping. For this reason, it is particularly well suited to mapping of the left ventricle, which must generally be accomplished quickly and with minimal trauma to the heart.
On the other hand, the methods and apparatus of the present invention are also suitable for mapping the other chambers of the heart, as well as for electrical mapping inside other cavities. For instance, the present invention is particularly useful for addressing transient events, as commonly occur in the atria of the heart. One such event is atrial tachycardia, which is a temporary, non-sustained paroxysmal rhythm. A probe in accordance with the present invention can be used to ascertain the effectiveness of therapy used in treating such a disorder. The probe can similarly be used to rapidly confirm the effectiveness of treatment for atrial flutter, for example, to verify that an ablation line or line of blockage is complete and has no gaps.
There is therefore provided, in accordance with a preferred embodiment of the present invention, a method for mapping electrical activity of a heart, including:
inserting a probe into a chamber of the heart, the probe including at least one position sensing device and a plurality of non-contact electrodes;
determining position coordinates of the electrodes relative to an endocardial surface of the chamber, using the at least one position sensing device;
measuring electrical potentials at the determined position coordinates using the electrodes;
computing electrical potentials at a plurality of points on the endocardial surface, using the measured potentials and the position coordinates; and
generating a map of electrical activity over the endocardial surface based on the computed potentials.
Preferably, inserting the probe includes positioning the probe such that the non-contact electrodes make substantially no physical contact with the endocardial surface.
Preferably, computing the electrical potentials includes finding an electric dipole strength at each of the plurality of points on the endocardial surface, responsive to the measured potentials. Further preferably, finding the electric dipole strength includes modeling the measured electrical potentials as being due to a superposition of respective electric dipole fields generated at the plurality of points on the endocardial surface, responsive to the determined position coordinates of the electrodes relative to respective position coordinates of the points. Most preferably, finding the electric dipole strength at each of the plurality of points includes deriving a system of equations expressing the measured potentials as a function of the superposition of dipole fields, and inverting the equations.
In a preferred embodiment, computing the electrical potentials includes acquiring a geometrical model of the endocardial surface, and finding a position of each of the electrodes relative to each of the plurality of points on the endocardial surface responsive to the geometrical model. Preferably, acquiring the geometrical model includes using the probe to generate the geometrical model. Most preferably, using the probe to generate the geometrical model includes bringing a distal tip of the probe into contact with a plurality of locations on the endocardial surface so as to determine position coordinates of the locations using the position sensing device, and generating the model using the position coordinates of the locations.
There is also provided, in accordance with a preferred embodiment of the present invention, apparatus for mapping electrical activity of a heart, including:
a probe, having a distal end configured for insertion into a chamber of the heart, the probe including, in proximity to the distal end, at least one position sensing device and a plurality of non-contact electrodes;
a processor, coupled to the probe so as to determine position coordinates of the electrodes relative to an endocardial surface of the chamber, using the at least one position sensing device, and to measure electrical potentials at the determined position coordinates using the electrodes, so as to compute electrical potentials at a plurality of points on the endocardial surface, using the measured potentials and the position coordinates; and
a display, coupled to be driven by the processor so as to display a map of electrical activity over the endocardial surface based on the computed potentials.
Preferably, the plurality of non-contact electrodes include an array of electrodes disposed over a surface of the probe in proximity to the distal end, so as to measure the electrical potentials substantially without physical contact with the endocardial surface.
Additionally or alternatively, the at least one is position sensing device includes a first position sensing device adjacent to the distal end of the probe and a second position sensing device in a position proximal to the first position sensing device and in proximity to the array of electrodes.
The present invention will be more fully understood from the following detailed description of the preferred embodiments thereof, taken together with the drawings in which: